Device and method for ultra-high temperature sterilization of an emulsion

ABSTRACT

A method for high temperature sterilization of an emulsion, in particular a dermocosmetic preparation. The method comprises the steps of gradually pre-heating, performing ultra-high temperature sterilization and gradually cooling the emulsion. The emulsion is heated up to a pre-heating temperature, which is the temperature of the emulsion at the stability limit. Ultra-high temperature sterilization is performed by infusion of the pre-heated emulsion by heating the emulsion up to a sterilization temperature, maintaining the emulsion at the sterilization temperature, and cooling the emulsion under a vacuum at an end-of-sterilization temperature. The emulsion is gradually cooled with agitation to a storage temperature.

The invention relates to a device and method for ultra-high temperaturesterilization of an emulsion, which is unstable at the sterilizationtemperature. It is, more specifically but not exclusively, suitable forsterilizing a dermocosmetic preparation in the form of gels, creams ormilks. More generally, the invention relates to a product in emulsion orsuspension form. Such products comprise at least two immiscible phases;one of the phases, called “internal” or “dispersed” phase, is insuspension and dispersed in the other, called “external” or “continuous”phase. In the products affected by this invention, the internal phase iscondensed or liquid and the external phase is liquid.

It is possible for such an emulsion to be “broken”, i.e. for it to loseits characteristics as an emulsion by various mechanisms such ascreaming, flocculation or coalescence. These phenomena, which sometimeslead to the destruction of the emulsion, are particularly sensitive tothe size of the particles in suspension and to the viscosity of theexternal phase. The finer the particles of the internal phase andequally, the more viscous the external phase, the stabler the emulsionwill be and vice versa. In a way, the stability is a measurement of thetime that said emulsion takes to lose its characteristics as anemulsion.

In many fields, such as cosmetics or pharmaceuticals, products in theform of an emulsion must meet preservation standards in regards ofmicrobial proliferation. One of the methods for ensuring thispreservation is to include preservatives in the product, such as estersof 4-Hydroxybenzoic acid, sorbates or glycol esters. These additivestake no part in the active substances required of the preparations thatcontain them; nevertheless they can be poorly tolerated. Therefore, itis preferable to propose products, in particular in the dermocosmeticsfield, that do not use such preservative additives, but whose shelf lifeand microbial cleanliness are adequate. To this end, said products mustbe sterile. Sterility is defined by standard EN 556 and the EuropeanPharmacopoeia in force as the probability of a microorganismproliferating in said product. Typically, said probability for a sterileproduct is below 10⁻⁶. The applicant has determined that for productstargeted by the invention, sterilization must be performed according toa method with a sterilizing value, F0, equal to 22 minutes. This valueF0 gives a time, expressed in minutes, that quantifies the lethal effectof humid heat at 121° C. on viable microorganisms; the method fordetermining it is defined by the European Pharmacopoeia in force. Aproduct that is sterile according to the definition of the EuropeanPharmacopoeia has been subjected to a sterilization method with asterilizing value F0 equal to at least 15 minutes. In practice, saidmethod may comprise several cumulative sterilization steps that do notuse only humid heat, but whose cumulated lethal effects are equivalentto this value F0.

The lethal effect is measured in relation to a reference germ:sporulated geobacillus stearothermophilus. These bacteria areparticularly heat-resistant and heat-tolerant. Thus, the targetsterilization effect is that which would have been produced on thesegerms, in the medium under study, by heat treatment at 121° C. for 22minutes. The time for this treatment increases exponentially as thetemperature decreases, depending on the type of microorganism that thetreatment is to destroy. Consequently, the following formula yields thevalue of F0:

F0=t·10^((T-121/z))

where:

-   -   t is the treatment time expressed in minutes;    -   z is a temperature scale and is defined by the heat resistance        of the microorganism under consideration. The value of z is        defined experimentally with regard to a parameter D. D is a        decimal reduction time, which measures the time required at a        given temperature, here 121° C., to reduce the concentration of        the microorganism under consideration by 90%. D equals one        minute for geobacillus stearothermophilus. Thus, z is the        temperature variation that changes the value by a factor of 10;        for geobacillus stearothermophilus, z equals 10° C.; these        factors, D and z, depend on the medium and in particular vary        according to the type of emulsion;    -   T is the treatment temperature.

Thus, a treatment with a sterilizing value equal to 22 is a treatmentthat is 22 minutes long at 121° C. (394 K), or a treatment that is 36seconds long at 135° C. (408 K).

Of course, heating in this way, which reduces viscosity of theemulsion's external phase considerably, has a destructive effect on thislast, such that heat sterilization treatments are proscribed by expertsand the use of additives or other methods is preferred. These othermethods, however, also have disadvantages or are not applicable:

sterilization by irradiation is difficult to implement and there aredoubts regarding the decay products;

sterilization by filtering membrane is not, in general, suitable forproducts as viscous as those used in dermocosmetics; in addition, it mayretain the internal phases when these are in condensed or solid state.Lastly, it does not support continuous processes or flow-ratescompatible with industrial-scale production of the product.

Document EP-B-2032175 describes a sterilization method, called UHT orUltra High Temperature, which can be adapted to the sterilization ofcosmetic products such as those targeted by the invention. The methodand the device described in this document use indirect heating of theemulsion, which is conveyed while kept under pressure in heating andcooling baths, through a tube. This tube ensures there is no contactwhatsoever between the products and the baths mentioned. This type ofmethod induces a thermal gradient between the product in contact withthe walls of the tube and the product at the center of the flow, andalso a thermal gradient between the start and end of the transit throughthe same bath. These characteristics make it difficult to check thelethal value of the sterilization thus performed. Therefore, with thismethod it is not possible to control strictly the durations of heating,plateauing at high temperature and cooling. In fact, the thinness ofsaid tube makes it difficult to achieve adequate flow-rates,particularly when the product to be sterilized is very viscous andbecause these durations are controlled by the flow-rate of the productthrough the tube. In addition, the heating and cooling of the productduring its travel into the tube change its viscosity, both along thetube and through its cross section; this makes controlling the pumpingof said product complicated and requires the use of high pressures.Furthermore, contact with the hot walls of the tube is likely to affectthe quality of the product negatively, whereas contact with said tube'scold walls, in the cooling zone, has a tendency to cause the fattysubstances within said product to solidify with no possibility ofsubsequent re-homogenization. Controlling this method is therefore adelicate matter and the results poorly reproducible. Lastly, this methodis not suitable for industrial-scale treatment of high volumes ofproduct, with flow-rates above 1 m³/hour.

Other ultra-high temperature treatment methods known from prior art, inparticular by infusion or injection, as applied to food products, arealso not very suitable for processing this type of product, and requirethe contact with steam to be realized when the product is in the liquidphase in order to achieve full effectiveness. Even though thesterilization properties required for food products are less stringentthan for the products targeted by the invention and even though theorganoleptic properties of food products that are treated usingultra-high temperature sterilization methods are less fragile than thestability of the emulsions targeted by the invention, it is common,according to prior art, to add surfactant additives to said products tostrengthen their stability in regard of the sterilization cycle. Thus,documents EP 0524751 and JP 2004 105181 describe methods of sterilizingfood emulsions, which food emulsions are stabilized beforehand by addingan ester. This type of surfactant additive is similar to preservatives,which the invention aims to eliminate.

To resolve the drawbacks of the prior art, the invention proposes amethod for continuous sterilization of emulsions, dermocosmeticpreparations in particular, at high temperature; this method comprisesthe following steps:

-   -   a. gradually pre-heating said emulsion up to a pre-heating        temperature T1, which is the stability limit of said emulsion;    -   b. performing ultra-high temperature sterilization by infusion        of said emulsion, thus pre-heated, which comprises:        -   i. heating up to a sterilization temperature T2;        -   ii. plateauing at the sterilization temperature;        -   iii. cooling under vacuum at an end-of-sterilization            temperature T3;    -   c. cooling gradually with agitation to a storage temperature T4.

Thus, the method that is the subject of the invention comprises, withinthe sequence of the process, phases of gradual heating and, above all,of gradual cooling, on either side of the sterilization operation. Thesegradual heating and cooling phases allow the following:

-   -   during heating, to bring the emulsion to a state of fluidity        suitable for the infusion sterilization method, without breaking        said emulsion;    -   during cooling, to recover the product characteristics as an        emulsion, which were partially degraded during the sterilization        operation.

The heating and cooling rates of steps i) and iii) of the sterilizationphase are imposed by the infusion method's thermodynamics.

The invention can be implemented according to the advantageousembodiments described below, which may be considered individually or inany technically effective combination.

Advantageously, with the temperatures expressed in degrees Kelvin,temperature T3 is lower than or equal to temperature T1, with thedifference between temperature T1 and temperature T3 less than 5K:

(T1−5)≦T3≦T1.

Thus the emulsion is rid of all the water absorbed during thesterilization by infusion phase but remains at a sufficient temperature,suitable for the subsequent cooling treatment.

Advantageously, cooling step c) is performed in plateaus, with a changein temperature between two plateaus of 15K (15° C.) at most. In thisway, respecting this condition avoids any thermal shock during cooling,which could degrade the emulsion.

Advantageously, cooling step c) comprises two plateaus carried out withmeans comprising a plate heat exchanger. Thus, respecting the plateausprevents the product coming into contact with walls that are too coldand that would cause the fatty substances to solidify, while allowing avolume of product compatible with industrial-scale applications to betreated.

Advantageously, temperature T2 is 418K (145° C.). This temperatureallows a sterilizing value F0=22 to be achieved in a sterilization timeof 6 seconds. The sterilization method results inevitably in a dilutionof the emulsion. Choosing these treatment conditions returns its initialproperties to the emulsion during the cooling phase and is, in addition,suitable for a broad range of dermocosmetic products.

Advantageously, temperature T1 is chosen to be 328K (55° C.). At thistemperature, most of the emulsions considered by this invention can beplaced in a state of fluidity suitable for passing into the UHT infusionsterilization device without degrading the emulsion.

From a practical point of view, and for industrial application of themethod, parameters T1, T2, T3 and the holding time are fixed,irrespective of the product; these correspond to thermodynamicequilibria that allow the rapid sterilization heating and cooling, aswell as the recovery of all the water absorbed by the emulsion duringthis process. The state of the emulsion after these first treatmentphases depends on the type of the products that were treated, but theselected parameters ensure that only the homogeneity of the emulsion isaffected by the treatment; this homogeneity is restored during thecooling phase; this phase is adjusted as to graduality and agitation forthe product in consideration.

To this end, the method that is the subject of the invention comprisesadvantageously a mechanical treatment step, called mixing, by shearingthe emulsion after sterilization step b).

Advantageously also, the method that is the subject of the inventionalso comprises a mixing step after the cooling step c).

These mixing steps allow the agitation rate of the emulsion necessary torestore its uniformity to be adjusted.

The invention also relates to a device for continuously implementing themethod that is the subject of the invention, which device comprises:

x. a UHT infusion sterilization device;

y. plate heat exchangers for pre-heating and cooling the emulsion to besterilized;

z. mechanical means of treating the emulsion by shearing at the exitfrom the UHT sterilization device.

Advantageously, the heat exchangers are of the type known as“scraped-surface”. In this way, the heat exchangers provide both theheating and cooling of the emulsion, without thermal shock when incontact with the walls; they also provide all or part of the agitationof the emulsion required to reinstate its uniformity.

Advantageously, the device that is the subject of the inventioncomprises two cooling scraped surface heat exchangers, which correspondto two cooling temperature plateaus. Thus, the first heat exchanger canbe set to a temperature sufficiently high to prevent the fattysubstances contained in the emulsion from solidifying when in contactwith the walls of said exchanger.

According to a particularly advantageous embodiment of the device thatis the subject of the invention, the latter comprises a disc-type mixingmachine at the outlet from the sterilization device, before the inlet ofthe first cooling scraped surface exchanger. Thus, said mixing machinecan homogenize the emulsion just after its cooling, when it is at arelatively high temperature, of the order of 323 K (50° C.) and stop anybeginning of coalescence, creaming or flocculation of said emulsion.

Advantageously, the device that is the subject of the inventioncomprises a disc-type mixing machine at the outlet from the last coolingheat exchanger. This characteristic, which can be combined with theprevious advantageous embodiment, perfects the homogenization of theemulsion to prevent any degradation of said homogeneity during thesubsequent operations.

Advantageously, the device that is the subject of the inventioncomprises, according to its embodiments that include disc-type mixingmachines, bypassing means to prevent the emulsion to be sterilized frompassing through said disc-type mixing machines. Thus, the cooling cycleand the amount of agitation can be adjusted, depending on the type ofemulsion being treated.

The invention also concerns an emulsion for dermocosmetic applications,which emulsion is sterile according to the EN 556 standard and theEuropean Pharmacopoeia, and, more specifically, with a sterility such asachieved for a sterilizing value F0=22. Such an emulsion, because of itslevel of sterilization, which is out of the reach of the methods knownfrom prior art, has exceptional preservation qualities without the useof preservation additives, which means that its tolerance can beimproved and also that active substances that are not compatible withthese additives can be used.

The invention is described below according to various preferred,non-limiting embodiments and with reference to FIGS. 1 to 3 wherein:

FIG. 1 shows a synoptic view of the implementation of a method accordingto an exemplary embodiment of the invention;

FIG. 2 is an example of a heat cycle and of the correlated change in theviscosity of a product being subjected to a treatment according to anexemplary embodiment of the invention; and

FIG. 3 is an example of the change in viscosity of an emulsion under theeffect of temperature to determine the stability limit temperature, FIG.3A at a temperature below this temperature, FIG. 3B at this temperatureand FIG. 3C at a temperature above this stability limit temperature.

FIG. 1: the markers designate the steps in the method as well as themeans of implementing this method during said steps. The product to besterilized is initially stored in the form of an emulsion in a tank(110). The treated products are mainly emulsions with an aqueousexternal phase and a fatty internal phase. As a non-limiting example,the method that is the subject of the invention is suitable forsterilizing and obtaining a sterile emulsion; said emulsion comprises anaqueous or continuous external phase, which comprises hydrophiliccomponents, in particular a carboxymethyl cellulose gel and an internalphase comprising oily matter and lipophile-modified polyacrylates. Themethod can nevertheless be applied to emulsions with a fatty continuousphase and an aqueous dispersed phase. The device and method that are thesubjects of the invention can be implemented for a wide variety ofemulsions, with viscosity ranging from 600 Cps to 45,000 Cps, i.e. fordermocosmetic products ranging from milk to balm.

Such emulsions are obtained by separating and breaking the drops of theinternal phase so as to create a uniform dispersion of these in theexternal phase. This dispersion is obtained by means of a mechanicaleffect: the mechanical energy thus introduced, e.g. by agitation orinjection, into the product is stored in the surface tension of thedrops at the interphases. The product is thus uniform when the size ofthe drops is substantially the same in all the emulsion. From thisemulsified state, the emulsion is broken when, by various mechanisms,the internal phase drops agglomerate until they again form two separatephases. In this case, the emulsion can only be formed by reintroducingthe mechanical energy, as was done initially. Between the initialemulsion and the broken emulsion, there are intermediate states forwhich the distribution of the sizes of the drops of the internal phaseis not uniform but in which, under defined thermodynamic conditions orwith a minimal introduction of mechanical energy, the emulsion can beagain homogenized. The method and device that are the subjects of theinvention aim to preserve at all times, particularly during the mostsevere phases of the treatment, the emulsion in a state that makes itpossible to achieve its re-homogenization easily. This treatmentprinciple is not known to the sterilization methods of emulsified foodproducts such as milk.

FIG. 2, which gives the temperature (210) and viscosity (230) of theemulsion as a function of time (220) allows the heat cycle (215) to befollowed correlatively with the viscosity (235) of the emulsion duringthe various steps (120, 130, 140, 160) of the method of the invention.

Going back to FIG. 1, pumping means (115) bring the product to betreated towards two scraped surface exchangers (121, 122) to take saidproduct, during a pre-heating step (120) to a temperature (T1), which isat the limit of the emulsion's stability. Temperature T1 is determinedby analyzing the change in the emulsion's viscosity as a function of thetemperature, as shown in FIG. 3.

FIG. 3: the analysis of the dynamic viscosity (320) of an emulsiondepending on its shearing rate (310) is given for increasing shearingrates, or shearing speeds gradients, that are increasing (301, 303, 305)or “outward” curve and for decreasing shearing rates (302, 304, 306) or“return” curve. This analysis, performed by means of a rheometercomprising a moving part (cylinder or cone) shearing the emulsionbetween the wall of said mobile part and a fixed wall, is performed atdifferent temperatures. Said analysis brings three characteristicbehaviors to the fore. According to the example of realization presentedin FIG. 3, the shearing rate (310) varies between 10 s⁻¹ and 150 s⁻¹.

FIG. 3A: for temperatures below temperature T1, the return curve (302)highlights lower viscosity values than the outward curve (301) for asingle shearing rate, because the moving part's shaking tends tofluidize the emulsion.

FIG. 3C: for temperatures above T1, the agitation, combined with theoutward (305) temperature destroys the emulsion, which is visible on thereturn curve (306) where viscosity falls.

FIG. 3B: when the test is performed at temperature T1, the viscosityvaries according to the outward (303) shearing rate but comes back tothe same viscosity after agitation of the moving part on the return(304).

Thus, temperature T1 can be determined by studying the rheologicalbehavior of the emulsion, depending on the temperature.

Going back to FIG. 1, the pre-heating step (120) advantageously usesscraped surface exchangers to provide simultaneously a very gradual anduniform rise in the temperature of the emulsion. Thus, the pre-heatingspeed is between 0.1° C.·s⁻¹ and 1° C.·s⁻¹.

The number of exchangers is chosen depending on the required flow-rate,to allow continuous treatment, suitable for industrial use. Thisflow-rate is in particular greater than 1 m³/hour. Such an exchangercomprises a stator and a rotor fitted with blades. The stator comprisesa double wall heated to the desired temperature by fluid circulation,such that the inner wall of the exchanger (121, 122) reaches the setpoint temperature T1. According to an advantageous exemplary embodiment,temperature T1 is chosen as 328K (55° C.). This temperature allows therequired emulsion fluidity to be obtained without degrading it. Therotor blades continuously scrape the inner wall of the exchanger, suchthat the instantaneous contact time of a volume of emulsion with saidwall is shortened; this avoids thermal shocks that can occur when thecold product comes into contact with the hot exchanger wall.

The gradual pre-heating step (120) is followed by the sterilization step(130). Sterilization is performed according to a method called “byinfusion”. This method consists of pulverizing a jet of the product intoan enclosed space filled with water steam at the desired temperature. Toperform this pulverization, the emulsion must be practically liquid.Since the exchange surface between the product drops and the steam isvery large, heating the product to the sterilization temperature T2 ispractically instantaneous in the entire volume of product injected intothe sterilization chamber. During this heating, the product absorbswater corresponding to the condensation of the quantity of steam thathas transmitted its heat to the product. The product is kept, during aplateauing step (132), at temperature T2, then directed towards a rapidcooling device (133). Advantageously, T2 is chosen as equal to 418K(145° C.), the plateauing time T, during the next step (132) is 6seconds. These conditions allow a sterilizing value of F0 equal to 22minutes to be achieved.

Sterilization (130) then proceeds to rapid cooling (133) called “flash”.The product, heated to temperature T2, is connected to a chamber (133)that was vacuum-filled by appropriate means (139). The product aspiredinto this chamber undergoes sudden decompression, which is accompaniedby a violent release of steam. The latent vaporization heat removesthermal energy from the product and thus cools it, by tearing dropletsaway. The thermodynamic cycle is regulated such that the water absorbedduring the heating in the first phase (131) of the sterilization cycleis recovered in the form of a condensate during the flash cooling cycle(133). Thus, temperatures T1 and T3 have to be close to each other andthe difference between T3 and T1 is adjusted according to the type ofproduct, and according to the resilience and appearance of the emulsion.Since the device that is the subject of the invention must be able totreat different types of products, the treatment temperatures T1, T2 andT3 are optimized so as to fulfill simultaneously all the sterilityrequirements, through the value of T2 and the plateauing time, dependingon the ability to re-homogenize the emulsion after the sterilizationtreatment, in particular through the choice of T1 and T3. Theseparameters are then fixed for the types of products to be treated. Thus,the applicant has determined an advantageous temperature T3, equal to323K (50° C.). Adjustments to the treatment for the specific product arerealized during subsequent phases (140, 150).

At the end of the sterilization step (130) and depending on the type ofproduct treated, a homogenization step (140) is realized, for exampleusing a disc-type mixing machine. This step aims to re-homogenize theemulsion quickly and to stop any coalescence phenomenon. Alternatively,a bypass valve (141) allows this homogenization step to be skipped formore stable products.

A gradual cooling step (150), using a plurality of scraped surfaceexchangers (123, 124), brings the emulsion back to a temperature (T4),close to or slightly higher than the ambient temperature to carry outthe storage of the emulsion for later packaging. The cooling speedduring this gradual cooling step is between 0.01° C.·s⁻¹ and 0.5°C.·s⁻¹.

Advantageously, T4 is chosen as 303K (30° C.), since emulsions are verystable at this temperature and sufficiently fluid for easy packaging.This temperature for storing in tanks also prevents emulsioncondensation phenomena inside said tank. The number of exchangers ineach of these sets is chosen depending on the foreseen flow-rate.

Cooling is realized in several steps, respecting the condition of amaximum interval of 15K (15° C.) between two successive plateaus. Thischaracteristic prevents the fatty drops of the emulsion's internal phasefrom solidifying when they come in contact with a wall that is too cold.If such solidification were to occur, said drops would become impossibleto divide and disperse in the external phase. Thus, starting fromT3=323K (50° C.) to finish at T4=303K (30° C.), cooling (150) isperformed in at least two steps. Thus, the device that is the subject ofthe invention comprises at least two exchangers, which correspond to twotemperature plateaus. The first scraped surface exchanger (123), or setof exchangers, is set to a temperature T′₄, which is just lower thantemperature T3. Thus, for a temperature T3 of 323K (50° C.), T′₄ ischosen to be equal to 313K (40° C.) and the second exchanger is set totemperature T4=303K (30° C.). Here too, using scraped surface exchangers(123, 124) helps prevent thermal shocks, while providing, for certainproducts, sufficient agitation to re-homogenize the emulsion. Thepractical number of exchangers is chosen depending on the flow-rate tobe achieved. Thus, two groups of exchangers corresponding to these twoplateaus can be installed in parallel or several exchangerscorresponding to closer thermal plateaus can be installed in series.

Depending on the type of product treated, a last mixing (145), forexample in a disc-type mixing machine, completes the homogenization ofthe emulsion. Alternatively, for other products, this step may beomitted, with a bypass valve (146) that connects the outlet of thesecond thermal exchanger (124) to the sterile buffer tank (160), beforethe product is packaged.

According to a first exemplary embodiment, the method that is thesubject of the invention is suitable for UHT sterilization of a productconsisting of an emulsion with an aqueous continuous phase and a fattyinternal phase, for example a product comprising:

water (Aqua),

a mineral oil such as paraffin oil (paraffinum liquidum),

glycerin,

glyceryl stearate,

squalane,

a carbomer,

and triethanolamine.

The method that is the subject of the invention allows this product tobe sterilized with a sterilizing value F0 of 22 minutes.

According to a second example of realization, the method that is thesubject of the invention is suitable for sterilizing a dermocosmeticproduct consisting 5%-50% of an oily continuous phase and an aqueousinternal phase, for example a product comprising:

glycerin,

xanthan gum,

(Di)Steardimonium Hectorite,

caprylic/capric triglycerides,

white beeswax,

evening primrose oil,

isopropyl palmitate,

PEG-30 Dipolyhydroxystearate,

citric acid monohydrate,

and water.

The method that is the subject of the invention allows this product tobe sterilized with a sterilizing value F0 of 22 minutes.

According to a third example of realization, the method that is thesubject of the invention is suitable for UHT sterilization of adermocosmetic product consisting of a surfactant medium with anionicamphoteric and non-ionic binary or ternary association, for example aproduct comprising:

zinc coceth sulfate,

disodium lauteth sulfosuccinate,

polysorbate 20,

Ceteareth-60 myristyl glycol,

lactic acid,

sodium hydroxide,

and water.

The method that is the subject of the invention allows this product tobe sterilized with a sterilizing value F0 of 22 minutes.

The description above and the exemplary embodiments show clearly thatthe invention has achieved the goals it envisages. In particular, itmakes it possible to realize in-depth, continuous sterilizationtreatment of a dermocosmetic product or of a fragile galenic preparationto bring them up to a sterility assurance level that allows said productto be preserved for a long time without adding preservatives.

1-18. (canceled)
 19. A method for high temperature sterilization of anemulsion, comprising the steps of: gradually pre-heating said emulsionup to a pre-heating temperature which is a temperature of said emulsionat a stability limit; performing ultra-high temperature sterilization byinfusion of said emulsion after it is pre-heated and comprising thesteps of: heating said emulsion up to a sterilization temperature;maintaining said emulsion at the sterilization temperature; cooling saidemulsion under a vacuum at an end-of-sterilization temperature; andgradually cooling said emulsion with agitation to a storage temperature.20. The method according to claim 19, wherein said emulsion is adermocosmetic preparation.
 21. The method according to claim 19, whereinthe end-of-sterilization temperature is lower than or equal to thepre-hating temperature, and a difference between the pre-heatingtemperature and the end-of-sterilization temperature is less than 5Kelvin (5K).
 22. The method according to claim 19, wherein the step ofgradually cooling is performed in plateaus with a maximum change intemperature between two cooling plateaus of 15K or 15° C.
 23. The methodaccording to claim 22, wherein the step of gradually cooling utilizes awall heat exchanger to obtain the two cooling plateaus.
 24. The methodaccording to claim 19, wherein the sterilization temperature is 418K or145° C.
 25. The method according to claim 24, wherein the pre-heatingtemperature is 328K or 55° C.
 26. The method according to claim 19,further comprising the step of mechanically processing said emulsionafter it is pre-heated by shearing said emulsion.
 27. The methodaccording to claim 19, further comprising the step of mixing saidemulsion after it is gradually cooled to the storage temperature.
 28. Adevice for continuous implementing the method according to claim 19,comprising: an UHT infusion sterilization device; plate heat exchangersfor pre-heating and cooling said emulsion to be sterilized; and amechanical device at an outlet of the UHT sterilization device fortreating said emulsion by shearing.
 29. The device according to claim28, wherein the heat exchangers are scraped surface type heatexchangers.
 30. The device according to claim 29, further comprising twocooling scraped surface heat exchangers to gradually cool said emulsionin plateaus with a maximum change in temperature between two coolingplateaus of 15K or 15° C., the two cooling scraped surface heatexchangers corresponding to two cooling plateaus.
 31. The deviceaccording to claim 30, further comprising a disc-type mixing machine atthe outlet from the sterilization device and before an inlet of a firstcooling scraped surface exchanger.
 32. The device according to claim 28,further comprising a disc-type mixing machine at an outlet of a lastheat exchanger.
 33. The device according to claim 31, further comprisinga bypassing device for preventing passage of said emulsion to besterilized into the disc-type mixing machine.
 34. The device accordingto claim 32, further comprising a bypassing device for preventingpassage of said emulsion to be sterilized into the disc-type mixingmachine.